Dielectric



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HTTRNEY- Junelz, 1945. s, RUBEN 23.7816@ l DIELECTRIC Filed oct. 22,1941 60 60 100 1Z0 :|40 160 :180 ZOO 220 TEMPERTURE- "F nimm y-esasreaimia 1945 i nmmc'raro Samuel Ruben, New llfochella-N. Y. lApplication october 2z, 1941, serial No. 415,999

9 claims. '(cr. zenssi This invention relates to an electrostatic denserand dielectrics therefor.

An object of the invention is to improve electrostatic condensers anddielectrics therefor. Another object is to improveV dielectricimpregnating materialsand provide a dielectric whichis vhomogeneous andnon-separating and which can be readily impregnated into the spacer` theapplication' contemplated. Most dielectric `materials `oi! comparabledielectric constant which have been used heretofore, such as lcastor oiland chlorinated diphenyl exhibit'such positive coefficients of 'powerfactor versus temperature.

` Purified coal tar resins such as coumarone, indene, cyclopentadieneand mixtures of these resins exhibit excellent high voltage breakdowncharacteristics and have 'been proposed as condenser dielectricmaterials. However, it is necessary to use theA high polymeric forms ofthese resins to obtain a suitably low powerfactorI and -high voltagebreakdown. The higheripolymerio forms, however, also have a high meltingpoint. In order to utilize these materials for impregnating condensers,it has 'therefore been necessary lto add liquid materials to lower thewithout departingfrom the spirit of the inven- In the drawing: Figure lis a graph containing curves of the capacity, power factor andinsulation resistance of a condenser embodying features ofthe presentinvention andcurves for comparison showing the power factor of certainrcondensers of the prior art; and Figures 2 and 3 illustrate a condenserembodying the present invention. f

A desirable dielectric-material for impregna-- tion into a porous spacerof an electrostatic con,- denser should preferably have a-highdielectric constant, low power factor, high insulation resistivity, highvoltage breakdown and should .be'

It is necessary un-A The power factor-temperatures coefficient plays ani'm- 'factor increases, the heat developed due to power factor lossesobviously also increases resulting inA a. runaway characteristic whichmust be allowed for by using a suiiiciently over-size condenser for f'neous dielectric.

vmelting point and reduce the 'viscosity of the composition when heatedto impregnating temperatures so that thorough impregnation of the porouscondenserl spacer may be achieved. Chlorinated benzene ring compoundsare examples of such plasticizing liquid materials and,

where high dielectric constant is not reguired,

tric properties deteriorate.

One of the major drawbacks ofdielectrics of this type, comprising aresin and a liquid plasticizer, is that they exhibitpower factor versustemperature curves having definite peaks at certain temperatures.y Themaximum value of power factor (where the curve has a peak) isdependentupon the melting point of the'mix'ture and this in turndependsv upon thel amount of plasticizer present. Informulating suchdielectric compositions, therefore, it is desirable that the percentageof plasticizer be adjusted to bring the power factor peak outside thenormal -operating temperature range of the condenser. This, oftenconflicts .with-the requirement that the dielectric shall have therequisite low viscosity at impregnating temperatures.

l I have now found a. means for overcoming these prior dimculties andproduced a' dielectric material which is heat stable, has a highdielectric constant, and can be vacuum impregnated without separation.My dielectric material prei'- erably comprises an eutectic mixture ofcoumarrone-indene or coumarone-indene-cyclopentadiene resin with ethylpentachlorbenzene (CaHsCls) Boiling range -deg. C-- 164-198 Specificgravity s 0.970.99 Dicyclopentadiene per cent 60-65 Indene do 15-20coumarone do- 5-10 Naphthalene up to do 2 Molecular weight 120-130Aniline point deg. C 26-27 This naphtha is heated to a temperaturebetween 200 andl 260 deg. C. for several hours which allows rapidpolymerization. Unreacted material and the lower polymers aresubsequently removed from the polymerized mass by combined steam andvacuum distillation. The average molecular weight of the resulting resin(about 500) has indicated `that the most probable composition is amixture of cyclopentadiene octamers, coumarone and indene tetramers anda small quantity of dimeric polymers which influence the melting point.

If the material is hydrogenated, its qualities are improved. Generally,it can-be used in the preparation of dielectrics of this invention inthe same proportions as the unhydrogenated form. The process ofhydrogenatlon of the resin is well-known and comprises reacting thepolymerized material with vhydrogen under pressure with heat andsometimes with a catalyst.

Ethyl pentachlorbenzene is a white crystalline solid having a meltingpoint of 57 deg. C. and a boiling pointl of 305 deg. C. The dielectricmay be produced by melting pure ethyl pentachlorbenzene containing notmore than 5% impurities or other materials, such as ethyltetrachlorbenzene, and the coumarone-indene-cyclopentadiene resintogether in eutectic proportions. A temperature of 125 C. is sumcienttomelt the ingredients and form a clear homogeneous liquid which, oncooling, remains a thick viscid liquid at room temperature instead ofreturning to a solid crystalline or brittle resin as were bothconstituents. The eutectic mixture occurs only within a certain range ofpercentage, namely between approximately 42% and 52% by weight of thecoumarone-indene-cyclopentadiene resin in the mixture. Between thesepercentages, a homogeneous viscid liquid dielectric is produced. Thecomposition will not separate under conditions of alternating currentoperation at commercial voltages such as 110 or 220 volts, and isstable, waterproof and substantially non-inflammable.

Due lto the fact that -there are several resin constituents in thedielectric mixture an exact eutectic point is. not distinguishable. Thematerial mixing them in the proportions required andA then heating themixture to about 125 C. with continuous stirring until a clear brownlliquid mixture is obtained and then allowing the mixture to cool. Theresulting eutectic mixture remains a very viscid liquid and upon heatingbecomes a free flowing liquid of low viscosity which penetrates readilyinto the paper spacers of a wound foil condenser assembly duringimpregnation.

Example 1 A eutectic mixture of 45% purified heat-polymerized coumaroneindene-cyclopentadiene resin and 55% ethyl pentachlorbenzene is producedin the manner described. This dielectric has the Example 2 A mixture of50% purified heat polymerized coumarone indene cyclopentadiene resin and50% ethyl pentachlorbenzene is produced in the same manner. This mixtureis homogeneous but is substantially hard at room temperatures. higherimpregnation temperature is required. The electrical properties are verysimilar.

Mixtures removed in proportional composition from lthe rangecontemplated by the present invention are generally poorly suited forcondenser dielectric purposes. They crystallize badly when cold,forming'a hetrogeneous structure of poor electrical character and lowelectric breakdown strength.

The accompanying graph of Figure 1 illustrates the electricalcharacteristics of the dielectric material when used in a condenser. Thecurves relate to a wound aluminum foil condenser spaced with kraft paperand impregnated with a dielectric composition consisting of 45% of theheat polymerized coumarone-indene-cyclopentadiene having a melting pointof 120 C. and 55% of the ethyl pentachlorbenzene. Curve I shows thechange in the power factor at 60 cyclesv of the material with increasingtemperature and illustrates that the power factor decreases as the temperature rises within the normal operating temperature range encounteredin operation on alternating current systems, such as in capacitor motorcircuits and for fluorescent lamp phase displacement purposes. Thisvcurve also shows the absence of power factor peaks such as occurs withliquid plasticized dielectrics. Curve 2 shows the capacity of thecondenser at various temperatures indicating very little change ofcapacity with temperature. Curve 3 shows the insulation resistance ofthe material in the condenser.

, Curves 4 and 5 illustrate for comparison the increasing power factorversus .temperature curves chlorinated diphenyl respectively.

l c 4stavamo g for condensers impregnated with castor oily andv Thecondenser can be formed as-illustrated in Y Figure 2 by rolling togethera pair of thin metal v foils 2| and 22, such as aluminum foil,interleaved f with double layer sheet spacers 23 'and 24 respectively.The sheet spacers may, for example, be

kraft paper or they may be processed regenerated cellulose lm. After thecondenser roll I is formed by windingthe foils and spacers together inthis manner the condenser roll or section I0 may be impregnated with themolten dielectric composition by immersion in the molten mixture at atemperature of about 110 C. A vacuum should be preferably be applied toobtain as low a. pressure as is possible' to permit thoroughimpregnation.

Figure 3 of .the drawing illustrates a completed condenser unitcomprising impregnated condenser section IIJ enclosed in a suitablefibre tube I I and embedded in a. moisture repellent insulatingl pitchor other insulating material I2. The foils .1

mixture l of vcoumarone-indexiefcycloperltadiene resin andethylpentachlorbenzene.

2.'A ldielectriccouiposedfof an 'eutectic mixture I' ofcoumarone-indene-cyclopentadene resin. and ethyl pentachlorbenzene.

'3. A dielectric material compri of 42% 'to 52% by-weight ofcoumarone-indeng- A'cyclopentadiene' resin and the balancesubstantially` all ethyl pentachlorbenzene; 10

4.'A delectric for electric condensers composed Y of a'mixture of 42% to52% by weight of coumarome-indenefcyclopentadiene resinpolymer sub-vstantially free of deleteriousimpuritiesand thebalance substantially.lall ethyl pentachlorbenzene.

. 5. A dielectric vfor electric condensers composed of a mixtureofapproximately 45% by weightof coumarone-'indenef cyclopentadiene,polymer resin substantially free of deleterious impurities and thebalance substantially allethyl pentachlorbenzene. 6.- '4

dielectric for electric condensers composed `of a` mixture ofapproximately 50% by weight of 2| and 22 of the condenser section maypreferably be wound in oset relation so that foil 2| projects fromone'end of the roll and foil 2i. from the other. Contact is then madewith the two foils by contact members l5 and I6 respectively. Contact .i

member I5 is connected by a suitable conductor to a soldering lug orterminal I3 attached to the closure disc closing one end of bre tube IIQi of the roll.

' mally solidpolymerof crude naphtha which con,-

Y -by Weight of couxnaror1eindene;cyclopentadieneA The present inventionaffords 'a meansof oli- V taining a condenser of relatively ,lowervolume and better operating characteristics than that aiorded bycondensers of the prior art.'

While the present invention, as to itsobjects and'advantages, has beendescribed herein Vas carried out in specic embodiments thereof, it isnot desired to be limited thereby but it is intended to cover theinvention broadly Within the spirit and scope of the appended claims.v 1

What is claimed is:

1. A dielectric materialcomprising an eutectic Acoumarcne-inde'necyclilpentadienegpolymer'v resin" substantially free ofdeleterious impurities andthe balance substantiallyall ethylpentacl'ilor'v benzene...v '7. A dielectric material composed of aneutectic" mixture of ethyl pentachlorbenzene and the nortains aboutto65% dicyclopentadiene, 15 to 20% indene and 5 to 10%coumaronevsubstantially free of deleterious impurities. 8. A dielectricmaterial composed otf-42'to 52% resin having` an Aaverage l-molecular'weight of aboutf500 and-comprising the polymer lof a crude naphthacontaining about 60 to' 65% dicyclopen' tadiene, 15 to 20% indene and 5.to 10% couma-` rone, and the balance substantially all ethylpentachlorbenzene. l.

9. A dielectric element for electrostatic conden sers comprising a sheetof porous s olid dielectric material and a viscid liquid dielectricheldthereinand composed ofan eutectic mixture ofcoumarone-indene-cyclopentadiene resin and ethyl pen'- sAMcEL RUBEN.

